System and method for transporting a compressed video and data bit stream over a communication channel

ABSTRACT

Digitally compressed video/audio bit streams, when transmitted over digital communication channels such as digital subscriber loop (DSL) access networks, ATM networks, satellite, or wireless digital transmission facilities, can be corrupted due to lack of sufficient channel bandwidth. This invention describes schemes to ensure lossless transmission of bit streams containing pre-compressed video signals within the communication channels. The schemes herein comprises a rate conversion system that converts the bit rate of a pre-compressed video bit stream from one bit rate to another, and that is integrated with a digital communication channel, and a means to convey the maximum channel transmission rate to the rate conversion system to allow satisfactory transmission of the bit stream from the input of the rate converter through the transmission facility.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application, pursuant to 35 USC §120,of prior U.S. patent application Ser. No. 09/741,451 entitled “A SYSTEMAND METHOD FOR TRANSPORTING A COMPRESSED VIDEO AND DATA BIT STREAM OVERA COMMUNICATION CHANNEL” by Zhang et al., filed on Dec. 19, 2000, theentirety of which is incorporated herein by reference for all purposes,which is a continuation application, pursuant to 35 USC §120, of U.S.patent application Ser. No. 08/947,480 entitled “A SYSTEM AND METHOD FORTRANSPORTING A COMPRESSED VIDEO AND DATA BIT STREAM OVER A COMMUNICATIONCHANNEL” by Zhang et al., filed on Oct. 10, 1997, the entirety of whichis incorporated herein by reference for all purposes, which claimsbenefit, pursuant to 35 U.S.C. §119, of U.S. Provisional ApplicationSer. No. 60/051,109, filed Jun. 26, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to communication channels andsystems for transmitting data. In particular, the present inventionrelates to a system and method for transmitting compressed digital videosignals over a communication channel. Still more particularly, thepresent invention relates to a system and method for transmittingcompressed digital video signals over digital subscriber loop (DSL)access networks and asynchronous transfer mode (ATM) networks.

2. Description of the Background Art

There are presently a variety of different communication channels fortransmitting or transporting video data. For example, communicationchannels such as digital subscriber loop (DSL) access networks, ATMnetworks, satellite, or wireless digital transmission facilities are allwell known. In fact, many standards have been developed for transmittingdata on the communication channels. The present invention relates tosuch communication channels, and for the purposes of the presentapplication a channel is defined broadly as a connection facility toconvey properly formatted digital information from one point to another.A channel includes some or all of the following elements: 1) physicaldevices that generate and receive the signals (modulator/demodulator);2) physical medium that carries the actual signals; 3) mathematicalschemes used to encode and decode the signals; 4) proper communicationprotocols used to establish, maintain and manage the connection createdby the channel. The concept of a channel includes but is not limited toa physical channel, but also logical connections established on top ofdifferent network protocols, such as xDSL, ATM, TCP/IP, wireless, HFC,coaxial cable, etc.

The channel is used to transport a bit stream, or a continuous sequenceof binary bits used to digitally represent compressed video, audio ordata. The bit rate is the number of bits per second that the channel isable to transport. The bit error rate is the statistical ratio betweenthe number of bits in error due to transmission and the total number ofbits transmitted. The channel capacity is the maximum bit rate at whicha given channel can convey digital information with a bit error rate nomore than a given value. And finally, a multiplex is a scheme used tocombine bit stream representations of different signals, such as audio,video, or data, into a single bit stream representation.

One problem with existing communication channels is their ability tohandle the transportation of video data. Video data is much larger thanmany other types of data, and therefore, requires much more bandwidthfrom the communication channels. Since transmission of video data withexisting communication channels would require excessive amounts of time,compression is an approach that has been used to make digital videoimages more transportable.

Digital video compression schemes allow digitized video frames to berepresented digitally in much more efficient manner. Compression ofdigital video makes it practical to transmit the compressed signal bydigital channels at a fraction of the bandwidth required to transmit theoriginal signal without compression. International standards have beencreated on video compression schemes. These include MPEG-1, MPEG-2,H.261, H.262, H.263, etc. These standardized compression schemes mostlyrely on several key algorithm schemes: motion compensated transformcoding (for example, DCT transforms or wavelet/sub-band transforms),quantization of the transform coefficients, and variable length encoding(VLC). The motion compensated encoding removes the temporally redundantinformation inherent in video sequences. The transform coding enablesorthogonal spatial frequency representation of spatial domain videosignals. Quantization of the transformed coefficients reduces the numberof levels required to represent a given digitized video sample and isthe major factor in bit usage reduction in the compression process. Theother factor contributing to the compression is the use of variablelength coding (VLC) so that most frequently used symbols are representedby the shortest code word. In general, the number of bits used torepresent a given image determines the quality of the decoded picture.The more bits used to represent a given image, the better the imagequality. The system that is used to compress digitized video sequenceusing the above described schemes is called an encoder or encodingsystem.

In the prior art compression schemes, the quantization scheme is lossy,or irreversible process. Specifically, it results in loss of videotextural information that cannot be recovered by further processing at alater stage. In addition, the quantization process has direct effect onthe resulting bit usage and decoded video quality of the compressed bitstream. The schemes at which the quantization parameters are adjustedcontrol the resulting bit rate of the compressed bit stream. Theresulting bit stream can have either constant bit rate, CBR, or variablebit rate, VBR. CBR compressed bit stream can be transmitted over channeldelivers digital information at a constant bit rate.

A compressed video bit stream generally is intended for real-timedecoded playback at a different time or location. The decoded real-timeplayback must be done at 30 frames per second for NTSC standard videoand 25 frames per second for PAL standard video. This implies that allof the information required to represent a digital picture must bedelivered to the destination in time for decoding and display in timelymanner. Therefore, this requires that the channel must be capable ofmaking such delivery. From a different perspective, the transmissionchannel imposes bit rate constraint on the compressed bit stream. Ingeneral, the quantization in the encoding process is adjusted so thatthe resulting bit rate can be accepted by the transmission channel.

Because both temporal and spatial redundancies are removed by thecompression schemes and because of variable length encoding, theresulting bit stream is much more sensitive to bit errors or bit lossesin the transmission process than if the uncompressed video istransmitted. In other words, minor bit error or loss of data incompressed bit stream typically results in major loss of video qualityor even complete shutdown of operation of the digital receiver/decoder.

Further, a real-time multimedia bit stream is highly sensitive todelays. A compressed video bit stream, when transmitted under excessiveand jittery delays, will cause the real-time decoder buffer to underflow or overflow, causing the decoded video sequence to be jerky, orcausing the audio video signals out of synchronization. Anotherconsequence of the real-time nature of compressed video decoding is thatlost compressed data will not be re-transmitted.

One particular communication channel that is becoming increasinglycommon is Asynchronous Transfer Mode (ATM) networks. ATM networks arebased on the ATM transport protocol which can be used to transport dataor multimedia bit stream with pre-specified quality of service. Unlikethe xDSL standard, ATM protocols specifies how data is first packetizedinto fixed sized data units, call cells. It also specifies how such acell stream can be multiplexed, de-multiplexed, switched and routedbetween different locations to support end-to-end connections at givenbit rate and/or quality of service (QOS). In ATM networks, data bitstream to be transported are first converted into fixed sized ATM cells,each cell has a 5 byte header and up to 48 bytes of payload. Ofparticular interests to our invention is the capability of ATM networksto carry MPEG transport streams.

In ATM networks, connections can be established with pre-determinedgrade of QOS. Conditions of network utilization, along with calladmission control sometimes may prevent new connection being establishedat the given bit rate or given quality of service. In such cases, therequested connection may either have to be rejected or a new set ofadmissible connection parameters have to be negotiated between thenetwork service provider and the user requesting the connection.

ATM networks can be used to carry either constant bit rate (CBR) orvariable bit rate (VBR) bit stream. The bit stream may be compressed bitstream or data. In either case, an agreement must be made between theuser requesting the connection and the network service provider. Theconnection agreement includes the bit rate profile of the bit stream andquality of service. If such an agreement cannot be reached, either theconnection must be rejected, or the bit rate profile must be modified,or the mismatched bit rates may cause periodic loss of data within theATM networks, which results in corrupted bit stream in thereceiver/decoder. Specific decoded video quality depends on the decoderdesign.

The process of modifying the bit rate profile of the input bit stream iscalled traffic shaping. The objective of the traffic shaping is tosmooth out the burstiness of the ATM cell stream so that the resultingbit rate profile is more constant than that without traffic shaping.Existing methods to do traffic shaping include using a large buffer tosmooth out the bit rate fluctuation, or to selectively drop ATM cellsduring high bit rate period. These methods were originally designed forconnections carrying data streams or non-real-time multimedia bitstream. In the case of using large buffers, data bit stream is notsensitive to large delay variations. In the case of selective celldropping, higher layer communication protocols will retransmit the lostinformation at a later time. However, in the case of transportingreal-time compressed video, none of the method is acceptable because ofthe tight constraint on the end-to-end delay variation. For example,when ATM networks are used to transport MPEG-2 transport stream, theend-to-end jitter typically shall not be more than 1 millisecond. Theuse of rate converter as traffic shaper will solve exactly this problem.

Within ATM networks data loss may also occur when there is not enoughchannel bandwidth to send all of the ATM cells. In this case, ATM cellsmay be dropped from the overflowing buffers. If the bit stream carriedin the connection complies with the connection agreement, such eventwill occur very infrequently and falls within the bounds of the qualityof service constraints.

Also, it is important to point out that in general compressed video bitstream are generated by either real-time encoders or pre-compressedvideo server storage systems, which are likely to be in a remote site,away from the network facility itself. This implies that in general itis difficult to encode the video signal with a resulting bit rateprofile tailored to the connection bandwidth available from the ATMnetwork.

ATM network protocols are under intense international standardizationeffort and several industry wide inter-operable specifications have beenproduced, including the one specific on means to carry MPEG-2 transportstreams over ATM networks using ATM Adaptation Layer 5 (AAL-5).

Therefore, there is a need for a system and method for transmittingdigital video information over data channels, that is simple toimplement and has smaller delay, and can match the input bit rate to thechannel bandwidth, resulting in a dramatically reduced bit error rate.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies and limitations of theprior art with a system and method for converting a bit stream of agiven bit rate to a different bit rate for reliable transport overcommunication channels. In various embodiments, the present inventionincludes: transmission of a compressed bit stream over AsymmetricDigital Subscriber Lines (ADSL) with rate adaptive capabilities (RADSL);transmission of a compressed bit stream over Asynchronous Transfer Mode(ATM) networks; flexible sharing of bandwidth of common communicationchannels among compressed bit stream and data traffic (including, butnot limited to, data stream based on the ATM protocols or TCP/IPprotocols, etc.); and statistical multiplexing of MPEG-2 transportstreams.

A preferred embodiment of the system of the present invention comprises:a bit rate converter, a transmitter, a physical medium, and a receiver.The bit rate converter is preferably coupled to receive an input signalthat is a video bit stream. The bit rate converter adjusts the bit rateof the input signal to match the communications channel and then outputsthe bit stream to the transmitter. The transmitter is in turn coupled tothe receiver by the physical medium. The transmitter send the bit streamover the medium to the receiver, where the bit stream is received. Thus,the system of the present invention advantageously eliminates the needto decode and encode the bit stream before transportation over thechannel. The bit rate converter eliminates the need for decompressionand compression and preferably comprises: a separation unit, a decoderand extractor, a plurality of modification units, an encoder and acombining unit. The bit rate converter essentially adjust the bit rateby making modifications to the video data portion of the bit stream. Thebit rate converter first separates the video data portion of the bitstream and then decodes and extracts the video data. The data is thenmodified to change the bit rate, and then encoded and combined with theother signals that make up the bit stream.

A preferred method for transporting data over a communication channelcomprises the steps of: converting a first bit rate of an input bitstream to a second bit rate, transmitting the bit stream at the secondbit rate; and receiving the bit stream at the second bit rate. Theconverting a first bit rate of an input bit stream to a second bit ratepreferably comprises the sub-steps of separating the bit stream intovideo, audio and data portions, decoding the video portion, extractingvectors and coefficients from the video portion, modifying the extracteddata, encoding the modified data, and combining the encoded video datawith the audio and data portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a prior art system for transmitting videodata over a communication channel;

FIG. 1B is a block diagram of a prior art system for transmitting videodata over a communication channel showing the encoding and decodingfunction in more detail;

FIG. 2A is a high level block diagram of one embodiment of a systemconstructed according to the present invention for transporting videodata;

FIG. 2B is a block diagram of the preferred system for bit rateconversion according to the present invention, depicted using terms andreference numeral similar to the prior art system of FIG. 1B to show theadvantages yielded by the present invention;

FIG. 2C is a block diagram of a first and preferred embodiment of asystem, constructed according to the present invention, for transportingvideo data including a communication channel;

FIG. 3 is a block diagram of a second embodiment of a system fortransporting video data integrated within the communication channel;

FIG. 4 is a first embodiment of a bit rate conversion device accordingto the present invention;

FIG. 5 is a second and preferred embodiment of a bit rate conversiondevice according to the present invention;

FIG. 6 is a block diagram of a system including a plurality of bit rateconverters for sending a single stream of video data over a plurality ofrespective channels;

FIG. 7 is a block diagram of a system including a plurality of bit rateconverters for sharing the bandwidth of a single communication channel;

FIG. 8 is block diagram of a system including a plurality of bit rateconverters for performing a statistical multiplexing for use of a singlecommunication channel;

FIG. 9 is a block diagram of a third embodiment of a system fortransporting video data integrated within the communication channel, inparticular, a rate adaptive asymmetric digital subscriber loop;

FIG. 10 is a graphical representation of the reference model used forthe ADSL transceiver unit-Central Office and the ADSL transceiverunit-Remote terminal;

FIG. 11 is a block diagram of a system using the rate conversion deviceof the present invention as an input point for an asynchronous transfermode (ATM) network;

FIG. 12 is a block diagram of a system integrating the rate conversiondevice of the present invention into an asynchronous transfer mode (ATM)switch; and

FIG. 13 is a block diagram of a system integrating the rate conversiondevice of the present invention into an ATM/ADSL communication device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1A, a prior art system 10 for transmitting videodata over a communication channel 19 is shown. The system 10 preferablyforms a channel 19 using an encoder 14, a transmitter 16, a receiver 20,a physical medium 18 coupling the transmitter 16 to the receiver and adecoder 22. The encoder 14 receives an input bit stream 32 andcompresses the input bit stream by encoding. The compress bit stream isthen received by the transmitter 16 and output over the physical medium18. The transmitter 16 can be any one of a variety of those known in theart for DSL networks or ATM networks. The signal sent over the physicalmedium 18 is received by the receiver 20 and input to the decoder 22.The decoder 22 restores the bit stream received by decompressing it intoits original format.

FIG. 1B shows a block diagram of a prior art system for transmittingvideo data over a communication channel showing the encoding anddecoding function in more detail. In particular, as shown, the encodingincludes receiving raw video data and processing the raw video data withmotion compensation 50, transform coding 52, quantization 54, and VLCencoding 54 to produce a compressed bit stream. The compressed bitstream can then, because of its reduced size, be transmitted over anyone of a variety of prior art transportation systems 58. The decodingprocess is then applied to the compressed bit stream received from thetransportation system 58 to obtain the original raw video images. Thedecoding includes VLC decoding 60, De-quantization 62, inverse transformcoding 64, and motion compensation 66, all in a conventional manner.

FIG. 2A is a high level block diagram of one embodiment of a system 250constructed according to the present invention for transporting videodata. The system preferably comprises a compression unit 252, a bit rateconverter 202, a transmission system 204 and an data formatting unit258. The compression unit 252 receives video data and other data andproduces a compressed bit stream. The compression unit may perform anyone of a variety of types of compression including but not limited toMPEG compression, H.26X or H.32X compression for video conferencing,compression using proprietary video stream formats, and compression ofnon-real-time data bit streams. Those skilled in the art will recognizethat the data formatting unit 258 is optional and provided only ifadditional data beyond the video data is being transmitted. The dataformatting unit 258 may add such additional data by either providing itto the compression unit 252 as just described or by providing itdirectly to the transmission system 204 as also shown in FIG. 2A. Thecompression unit 252 provides a compressed bit stream to the input ofthe bit rate converter 202. The bit rate converter 202 advantageouslyadjust the bit rate to match the bandwidth of the transmission system204. The bit rate converter 202 in its various embodiments will bedescribed below in more detail, however, the bit rate converter 202 canperform conversion by adjusting or modifying the encoded bit streamsyntax such as for the VLC decoding, the de-quantization, the inversetransform coding or the motion compensation. The output of the bit rateconverter 202 is provided to the transmission system 204 which formatsthe data and transmits it over a physical channel (not shown). Thetransmission system 204 may be any one of a number of conventionaltransmission systems, including but not limited to ASDL, ATM/ADSL, ATM,ISDN links, Ethernets, public data networks, T1, T3, DS-3, OC-3,wireless/terrestrial networks, digital satellites, and digital cablenetworks, and particular ones are described below.

FIG. 2B is a block diagram of the preferred system for bit rateconversion according to the present invention, depicted using terms andreference numeral similar to the prior art system of FIG. 1B for ease ofunderstanding and to show the advantages yielded by the presentinvention. In particular, the FIG. 2B is annotated with arrows to showthe advantages of the present invention. As shown in FIG. 2B, the bitrate converter 204 includes a process of decoding, bit rate converting,and encoding in the compressed domain. However, based on themodification units (see FIGS. 4 and 5 below) used in the bit rateconverter 204, the bit rate conversion process effectively follows oneof the paths specified by arrows A, B, C or D. Generally, motioncompensation is most computationally expensive, transform coding andinverse transform coding are also quite expensive. In general, withoutspecial hardware to perform these functions, motion compensation andtransform coding will take over 80%-90% of the overall decode-encodecomputation load. The key to a simplified rate conversion schemeaccording to the present invention is therefore to bypass some of theseexpensive steps. For example, in FIG. 2, if we take the path B, motioncompensation is avoided. If we take path C, both motion compensation andtransform coding are eliminated. If we take path D, quantization stepsare also eliminated, in addition to motion compensation and transformcoding. Of course, if we take path A, the entire decoding and encodingprocesses are performed, resulting in the most flexibility and qualitypotential, at the cost of being most expensive. Each of these paths canbe specified by the use of different modification units, 404, 406, 408,514, 516, 518 as will be described below with reference to FIG. 4 andFIG. 5.

While the present invention will now be described in the context of anAsymmetric Digital Subscriber Loop (ADSL) and ATM networks, thoseskilled in the art will realize that the present invention is applicableto a variety of other types of communication channels such as any xDSLincludes ADSL, HDSL, VDSL, SDSL.

Asymmetric Digital Subscriber Loop, or ADSL, is a physical line codemodulation scheme for transmitting digital bit stream over a single pairof plain old telephone system (POTS) grade twisted copper wires, thatare usually noisy and are subject to outside interference. Severalschemes have been developed to achieve high channel capacity of the saidtwisted copper wires. xDSL systems provide simple or full duplex raw bitpipes between the Central Office (CO) and the remote site receivers. Thematerial content and the format of the bit stream or the protocols usedby the connections being established by the bit pipe is immaterial tothe xDSL system itself. In ADSL, the downstream link, from CO to remotesite, has higher bandwidth than the upstream direction. Downstreamchannel capacity is typically up to 8 Mbps, and upstream channelcapacity is up to about 1 Mbps; the actual channel capacity depends onthe noise level of the wires and the distance between the transmitterand the receiver.

Because broadcast video quality can be achieved with compressed video,such as MPEG-2, at 3-6 Mbps, ADSL provides an ideal delivery scheme forcompressed digital video and other high speed data connecting COs withremote sites, which can be either consumer subscribers or businessestablishments.

However, because of the variation in physical line conditions due toboth the physical distance of the connection and the noise conditions ofthe lines, the ADSL transmission schemes do not specify channel capacityin either direction, rather the channel capacity is determined atconnection set up time via channel initialization and training by thetransceivers at the CO location and at the remote locations, in aconventional manner. The initialization and training process determinesthe proper coding configuration best matched to the current channelcondition in order to achieve the maximum channel capacity. During theconnection, due to change in line condition or due to loss of data, thetransceivers may also re-initialize and retrain to settle on the newcoding configuration.

In all the ADSL figures and discussions for the present invention below,it is important to point out that the ADSL channel is bi-directional,even though the present invention is described and shown by focusing ona single direction for ease of understanding. The present inventionfocuses on the transmission in a direction from a central office to acustomer as shown in FIGS. 2 and 9 from 210 to 214. In other words, thetransmitter device (such as transmitter 906) is also a receiver devicein the reverse direction, from the customer to the central office (from208 to 206). For video over ADSL, the bit rate conversion over ADSL inthe customer to central office direction appears pedantic butconceptually possible, though at a lower maximum bit rate. Still moreparticularly, if transmitter 906 in FIG. 9 is a transmitter as part ofATU-C (central office), then it must also be a receiver as part of ATU-C(remote). If box 906 is treated as part of an ATU-R then the endsubscriber is sending bit rate converted video up-stream to centraloffice.

Referring now to FIG. 2C, a first and preferred embodiment of a system200 for transporting digital video data constructed according to thepresent invention is shown. The system 200 preferably comprises a bitrate converter 202 and a channel 204. The channel 204 is furtherincludes a transmitter 206 coupled by a physical medium 18 to a receiver208. This embodiment of the system 200 is particularly advantageousbecause, as can be seen from FIG. 2C, the need for the encoder anddecoder is eliminated. The bit rate converter 202 simply adjusts the bitrate output to match the capacity or bandwidth of the channel 204. Morespecifically, the bit rate converter 202 has an input coupled to line210 to receive an pre-compressed signal of digital video data. The bitrate converter 202 adjust the bit rate at which the bit stream isprovided to the transmitter 206. The output of the bit rate converter202 is coupled by line 212 to the input of the transmitter 206. Theoutput of the transmitter 206 is coupled by the physical medium 18 tothe input of the receiver 208. The physical medium may be any one of avariety of types, but is preferably twisted pair. The output of thereceiver 208 is coupled to line 214 and provides the output signal whichis also a compressed signal but with a different bit rate. Asillustrated in FIG. 2C, the bit rate converter 202 and the transmitter206 are separate devices or if performed in software separate modules.

Referring now to FIG. 3, a block diagram of a second embodiment of asystem 300 for transporting video data integrated within thecommunication channel 300 is shown. In the second embodiment 300, thebit rate conversion device or converter 304 is integrated with thetransmitter 306 to form a single device 302. Like the first embodiment,the second embodiment 300, receives a pre-compressed signal on line 210.Line 210 is coupled to an input of the bit rate conversion device 304.The output of the bit rate conversion device 304 is in turn coupled tothe input of the transmitter 306 by line 308. The output of thetransmitter 306 is likewise coupled to the physical medium 18 and thereceiver 208. This embodiment 300 is particularly advantageous becauseit allows integration of the bit rate conversion with the transmitterinto a single high performance DSP device.

Referring now to FIG. 4, a first embodiment of a bit rate conversiondevice 202 a/304 a according to the present invention is shown in moredetail. The present invention advantageously uses bit rate conversion tomatch the rate of the bit stream to the capacity of the channel 204. Bitrate conversion of compressed video bit stream refers to the processperformed on a pre-compressed video bit stream which, when applied tothe bit stream, results in a different bit usage than the originallycompressed bit stream. In a typical scenario (see FIG. 2C), the new bitrate is smaller than the original bit rate, but sometimes the resultingbit rate can also be greater than the original bit rate. When thedigital video is first compressed, the encoder must assume a particularbit rate profile, whether it is constant bit rate (CBR) or a variablebit rate (VBR). The word “profile” refers to the fact that bit rate maynot be constant, but variable under certain constraints, such as peakbit rate, average bit rate, minimum bit rate, etc. For example, aconstant bit rate stream at 4 Mbps does not have the same bit rateprofile as a variable bit rate stream at an average of 4 Mbps but haslarger maximum bit rate and smaller minimum bit rate, respectively. Inother scenarios (see FIGS. 6 and 7), the compressed bit stream may bedelivered to different transmission channels each having a differentchannel capacity, or the compressed bit stream may be furthermultiplexed with other bit streams to share the same channel capacity.For example, a compressed video stream at 6 million bits per second, or6 Mbps, may need to be transmitted over a channel capable of deliveringonly, say, 5.5 Mbps. Therefore, if the same bit stream is transmittedover the channel, 0.5 Mbps must be removed before the transmission. Asdescribed earlier, arbitrarily removing the bits from the compressed bitstream is not acceptable. The bit rate conversion process is intended toremove bits from the compressed bit stream so that the resulting bitstream is still compliant to the given compression syntax, thus can bedecoded by the receiver, albeit at a possibly lower quality than theoriginally compressed bit stream.

Even though a compressed bit stream typically comprises a combination,called a multiplex, of compressed audio, video and auxiliary data bitstreams, the bit rate conversion process described in this inventionrefers specifically to procedures applied on compressed video bitstream. There are several ways to increase or decrease the bit rate ofpre-compressed video bit stream. The present invention can alternativelyuse any one of the following methods for bit rate conversion.

-   -   1. Removing or insertion of filler packets/frames (in the case        of MPEG-2 transport streams the filler packets are null        transport packets);    -   2. Removing or inserting stuffing bits into the compressed video        stream (in the case of MPEG, H.261, H.262 or H.263, stuffing        bits can inserted or removed at the end of the encoded video        frames);    -   3. Parsing and extracting the DCT coefficients, generate        variable length codes, and re-combine them with the motion        vectors in the originally compressed bit streams. In addition,        reference frames may optionally be reconstructed in the        frequency domain and re-quantization is performed.    -   4. Discarding data used to represent selected video frames and        generate frame repeat information in the bit stream so that the        resulting bit stream contains information to instruct the        decoder to repeat the dropped frames to maintain continuous        display;    -   5. First decode the bit stream into analog video frames and then        encode the video frames back at a different bit rate suitable        for transmission.

As best shown by FIG. 4, a first and preferred embodiment for the bitrate converter 202 a/304 a comprises: a separation unit 400, a decoderand extracter 402, a plurality of modification units 404, 406, 408, anencoder 410, a combining unit 412 and a rate controller 430. While thepresent invention will now be described as an apparatus composed ofunits, those skilled in the area will recognize that the presentinvention encompasses a method, process or software having as steps theactions performed by each unit and described below.

The separation unit 400 has an input and a plurality of outputs. Theinput of the separation unit 400 is coupled to line 210 to receive aninput of pre-compressed digital video bit stream. The separation unit400 preferably de-multiplexes the system layer stream, removing fillerpackets/frames as appropriate, to obtain the video bit stream, the audiobit stream and a data bit stream. The video bit stream is provided on afirst output coupled to line 420, the audio bit stream is provided on asecond output coupled to line 422, and a data bit stream is provided ona third output coupled to line 424. Those skilled in the art willunderstand the operation of the separation unit 400, based on theprotocol being used for the bit stream. Based on the protocol, the bitstream can divided into the sub-streams according to the presentinvention.

The input of the decoder and extracter 402 is coupled to line 420 toreceive the video signal from the separation unit 400. The decoder andextracter 402 preferably parses all timing, programming and otherauxiliary information and removes all stuffing data bits as appropriate.This parsing step produces a number of streams that in turn need to bedecoded. In the preferred embodiment, three streams are produced, onefor transform coefficients, one for motion vectors, and a final one forauxiliary information bits. The decoder and extracter 402 then decodeseach respective stream with a suitable decoder, such as variable lengthdecoding. Each of the decoded streams is provided on a respective outputof the decoder and extracter 402.

As shown in FIG. 4, the plurality of outputs of the decoder andextracter 402 are each coupled to a respective modification unit 404,406, 408. The modifications units 404, 406, 408 are used to reduce thenumber of bits needed for the transform (such as discrete cosinetransform) coefficients, motion vectors, and other auxiliary informationbits. As has been noted above, any one of a variety of methods can beused to modify the number of bits used to represent each portion ofinformation for the three types, and thereby adjust the bit rate of thestream. The modification units 404, 406, 408 are controlled by the ratecontroller 430. The rate controller 430 has an input and an output. Theinput of the rate controller 430 is coupled to line 434 to receive acontrol signal indicating the amount of conversion or the desired outputbit rate for the bit rate converter 202 a/304 a. For example, line 434may be coupled to line 912 to receive a rate value from a RADSLtransmitter 906 in an ADSL embodiment or to line 1112 to receive a ratevalue from an ATM network 1106 in an ATM environment. The ratecontroller 430 provides a control signal to each of the modificationunit 404, 406, 408 via line 432 (shown by diagram as a dashed box). Thecontrol signal specifies the amount of modifying each of themodifications units 404, 406, 408 performs to achieve the desired outputbit rate from the bit rate converter 202 a/304 a. The modification units404, 406, 408 may be similar to those described below for FIG. 5.

The output of each of the modifications units 404, 406, 408 is coupledto the respective input of the encoder 410. The encoder 410 preferablyperforms variable length coding of all the bits, and then outputs theencoded stream on line 426.

The combining unit 412 has three inputs that are respectively coupled tolines 426, 422 and 424, to receive the encoded stream, an audio streamand a data stream. The combining unit 412 preferably performsmultiplexing of the bits back into compliant bit stream and insertstuffing bits, filler packets as appropriate. The output of thecombining unit 412 is coupled to line 212 and forms the output of thebit rate converter 202 a/304 a. The output of the combining unit 412provides a signal that is converted to match the rate of the channel.

Referring now to FIG. 5, a second and preferred embodiment of a bit rateconversion device 202 b/304 b according to the present invention isshown. The bit rate conversion device 202 b/304 b is adapted for use ona MPEG-2 transport stream. The second embodiment of the bit rateconversion device 202 b/304 b preferably comprises a separation unit500, a de-multiplexer 502, a elementary stream bit parser 504, a DCT VLCdecoder 506, a motion vector VLC decoder 508, an auxiliary informationdecoder 510, a rate controller 512, a plurality of modification units514, 516, 518, a DCT VLC encoder 520, a motion vector VLC encoder 522,an auxiliary information encoder 524, a stream bit multiplexer 526, anda transport multiplexer 528.

The separation unit 500 first receives the pre-compressed video datastream. The separation unit 500 is similar as has been described above,and produces a video transport stream, an audio stream, and an datastream. The audio stream and data stream are output directly to thetransport multiplexer 528 which recombines these streams with the rateconverted video.

The de-multiplexer 502 is coupled to receive the video stream from theseparation unit 500. The de-multiplexer 502 extracts a video elementarystream payload from the video transport stream and in turn sends thevideo elementary stream payload to the elementary stream bit parser 504.The elementary stream bit parser 504 receives the output of thede-multiplexer 502 and divides it into a transform coefficientcomponent, a motion vector component, and an auxiliary informationcomponent. Each of these components is output to a respective decoder506, 508, 510. For example, the discrete cosine transform (DCT) variablelength coding (VLC) decoder 506 is provided for the transformcoefficient component, the motion vector (MV) variable length coding(VLC) decoder 508 receives the motion vector component, and theauxiliary information decoder 510 receives the auxiliary informationcomponent.

As shown in FIG. 5, each of the modification units 514, 516, 518 iscoupled to a respective decoder 506, 508, 510 as the source ofinformation to be modified. The present invention also provides the ratecontroller 512 to control the bit rate at which the transportmultiplexer 528 outputs data. The rate controller 512 preferablydetermines the bit usage of each video frame so that the resultingoutput bit stream maintains a desired bit rate profile. In the case ofCBR video, the rate controller 512 ensures that the resulting outputcompressed bit stream can be delivered via a constant bit rate channelunder the standard decoder buffer constraint. The present inventionperforms rate control by adjusting the quantization factor embedded inthe video bit stream, however, those skilled in the art will realizethat other methods of rate control could be used. The rate controller512 is preferably coupled to receive commands that specify the rate forthe output stream, and therefore, the rate by which the modificationunits 514, 516, 518 must adjust the input data streams. For example,when the rate controller is used in the context of RADSL, the input tothe rate controller 512 is coupled to line 532 which in turn is coupledto receive feedback from an RADSL transmitter or ADSL modem to controlthe target output bit rate such as the one shown in FIG. 9 (e.g., line532 is coupled to line 912). In such an arrangement, the signal providedon line 532 is a value or rate for the modification units 514, 516, 518to output data. The rate controller 512 is shown diagrammatically inFIG. 5 as being coupled to all three of the modification units 514, 516,518 by control signal line 530. While the rate controller 512 has beendescribed as being a discrete device, those skilled in the art willrealize that the rate controller 512 could be software that provides acontrol signal to the modification units 514, 516, 518.

The modification units 514, 516, 518 can be used to provide a variety ofbit rate conversions, and the present invention is not limited to theones detailed below. The modification units 514, 516, 518 are used tomodify the encoded bit stream syntax and bit usage. In addition to thefunctionality already discussed in the application, other functions themodification units 514, 516, 518 may perform include and involvemodules, such as:

-   -   1) Selectively scaling or setting transform coefficients to zero        (equivalent to filtering) using modification unit 514, then        encoding the transform coefficients back into VLC using the DCT        VLC encoder 520, to produce a different bit rate at the output        of the transport multiplexer on line 305. This approach        corresponds to taking the processing path D in FIG. 2.    -   2) selectively discarding entire coded frames using the decoders        506, 508, 510 and modification units 514, 516, 518 to produce a        different coded video frame rate. This approach corresponds to        taking the processing path D in FIG. 2.    -   3) Extracting and changing the quantization scale factors using        the auxiliary information decoder 510 and the modification unit        518, and then using the changed quantization scale factors to        encode transform coefficient back into VLC with the encoders        520, 522, 524, to produce a different bit rate usage at the        output of the transport multiplexer on line 305. This approach        corresponds to taking the processing path C in FIG. 2.    -   4) Completely decoding the bit stream and performing inverse        transform coding (such as inverse DCT), however, preserving the        same motion vectors extracted from the input bit stream using        the MV VLC decoder 508, and then using the motion vectors to        perform predictive motion compensated encoding, performing        transform coding (such as DCT), followed by VLC coding with the        DCT VLC encoder 520 to produce a bit stream at a different bit        rate. This approach corresponds to taking the processing path B        in FIG. 2. This approach would also require the addition of an        inverse DCT module coupled between the DCT VLC decoder 506 and        the modification unit 514, and the addition of a DCT module        coupled between the modification unit 514 and the DCT VLC        encoder 520. Essentially, in this approach, the modification        unit 514 is performing image reconstruction and motion residual        construction.    -   5) Changing the resolution of the video images by directly        re-mapping the decompressed transform coefficients from one        resolution to another using modification unit 514 and then        encoding the resulting coefficients back into VLC using encoders        520, 522, 524. This approach corresponds to taking the        processing path B in FIG. 2.    -   6) completely decoding the bit stream, adding low pass spatial        filtering to the decoded digitized video images and re-encoding        them back to compressed forms, to produce a lower bit rate. This        approach corresponds to taking the processing path A in FIG. 2.

The outputs of the modification units 514, 516, 518 are in turn coupledto respectively to the DCT VLC encoder 520, the motion vector VLCencoder 522, the auxiliary information encoder 524. Each of the encoders520, 522, 524 codes the data back into the compressed format. Theoutputs of the encoders 520, 522, 524 are then combined by stream bitmultiplexer 526, and then again combined with the audio and data by thetransport multiplexer 528. Those skilled in the art will recognize fromFIGS. 4 and 5 that the present invention can be applied to bit streambased on other transform schemes, and MPEG-2 is used only by way ofexample.

Referring now to FIGS. 6, 7 and 8, three systems where the rateconverter/channel combination of the present invention is particularlyadvantageous will be described. The present invention focuses on schemesthat combine rate conversion with the transmission channel. Thecombination allows lossless transmission of rate converted bit streameven when the original bit rate and available channel capacity aremismatched. The combination also enables flexible bandwidth sharingbetween the given bit stream and other data bit streams.

Referring now to FIG. 6, a block diagram of a system 600 including aplurality of bit rate converters 604, 606, 608 for sending a singlestream of video data over a plurality of respective channels 610, 612,614 is shown. In some multimedia delivery systems, compressed videoprograms are delivered to numerous digital receiver/decoders via one ormore digital transmission channels. In such multi-cast situations, thesame compressed video bit stream 602, which has a predetermined bit rateR, must be delivered to different end receiver/decoders via differentchannels 610, 612, 614, and some of the channels 610, 612, 614 may nothave a capacity sufficient to transmit the digital stream at therequested bit rate R. In these cases, the present invention applies thebit rate conversion process to the originally compressed bit stream sothat the resulting bit rate is no more than the channel capacity. Thesystem 600 preferably provides a respective bit rate converters 604,606, 608. Each of the bit rate converters 604, 606, 608 is preferablyadapted to convert the incoming original compressed bit stream to a bitstream with a rate that is appropriate for the respective channel 610,612, 614 since each different channel 610, 612, 614 can have differentcapacity. For example, if the first channel 610 has a channel capacityR1, which is less than R, the bit rate converter 604 converts theoriginal compressed bit stream to have a rate that matches the channel610 capacity, namely R1. Similarly, if the second channel 612 has acapacity R2, where R2 is less than R but greater than R1, the bit rateconverter 606 converts the original compressed bit stream to have a ratethat matches the channel 612 capacity, namely R2. Finally, if the thirdchannel 614 has a capacity R3, and R3 is equal to R, then the bit rateconverter 608 simply passed the original compressed bit stream throughthe channel 614.

Referring now to FIG. 7, a block diagram of a system 700 including aplurality of bit rate converters 702, 704 for flexible sharing thebandwidth of a single communication channel 708 with other types of datastreams is shown. In some multimedia delivery systems, extraneous bitstream data may arrive at the facility and must be multiplexed with theexisting bit stream before being delivered to the receiver/decoder.However, the total available channel bandwidth may not be sufficient toaccommodate the combined bandwidth requirement. In this case, bit rateconversion process may be applied to the originally compressed video bitstream so that the resulting combined bit rate is no more than thechannel capacity. Such a system 700 includes a first bit rate converter702, a second bit rate converter 704, a multiplexer 706 and a channel708. The first bit rate converter 702 is preferably coupled to receive afirst original compressed video stream and output a rate modified bitstream to the multiplexer 706. The second bit rate converter 704 ispreferably coupled to receive a second compressed video stream or datastream and outputs a second rate modified bit stream to the multiplexer706. The multiplexer 706 combines the two inputs and outputs a singlebit stream over the channel 708. According to the preferred embodimentof the present invention, the output of the first bit rate converter 702and the second bit rate converter 704 are such that when they aremultiplexed together they are less than or equal to the capacity of thechannel 708. Therefore, by performing bit rate conversion on the twoincoming streams, the present invention ensures lossless transmissionsince the channel capacity will not be exceeded. More particularly, themultiplexer 706 determines an intended bit rate profile for the firstbit stream so that the converted bit rate is less than available channelbandwidth to allow the second data stream to take up any remainingbandwidth. The multiplexer 706 preferably includes a scheme that giveshigher priority to the first bit stream so that when there isinsufficient bandwidth, the second data bit stream is discarded. Forexamples, such a scheme is particularly advantageous where a timecritical bit stream is provided to the first bit rate converter 702 suchas real-time compressed video, and non time-critical data is provided tothe second bit rate converter 704 such as a TCP/IP based data stream.Essentially, the lower priority data stream picks up the slack bandwidthleft over by the high priority bit stream. The multiplexer 706 firstdetermines bandwidth given to the real-time bit stream, it then uses thepriority scheme to provide leftover bandwidth to the second data stream.

Referring now to FIG. 8, yet another application of the presentinvention is shown by the block diagram of a system 800 including aplurality of bit rate converters 802, 804, 806 for performing astatistical multiplexing for use of a single communication channel 810.In some applications, such as a satellite transponder, the analogspectrum of a coaxial cable is used to transmit digital video, or awireless channel may be used to carry multiple compressed bit streams.In these cases, a multiplexing scheme must be used to allow logicalsharing of the same channel bandwidth. If all of the bit streamsparticipating in the multiplexing comply with the compression systemlayer standard, such multiplexing can be achieved within the compressionsystem layer. Otherwise, the bit stream must be multiplexed usingdifferent schemes. The need for bit rate conversion arises when the sumof the individual bandwidths does not fit into the available channelcapacity. In this case, the bit rate conversion scheme adjusts thecompressed video bit stream in the multiplex such that the resultingmultiplexed bit stream has a total bit rate no greater than the channelcapacity. This process is called statistical multiplexing because ingeneral the bit rate usage of an individual bit stream is notdeterministic, but bit rate fluctuations compensate among different bitstreams to achieve a constant channel bandwidth usage. As shown in FIG.8, the preferred embodiment of such a system 800 comprises a pluralityof bit rate converters 802, 804, 806, a statistical multiplexer 808 anda communication channel 810. Each of the bit rate converters 802, 804,806 is preferably coupled to receive a respective original compressedbit stream and outputs a rate converted bit stream. Each of the bit rateconverters 802, 804, 806 has its output coupled to an input of thestatistical multiplexer 808 to provide the rate converted bit streams.Each of the bit rate converters 802, 804, and 806 also has another inputcoupled to receive feedback from the statistical multiplexer 808 vialines 812, 814 and 816, respectively. The statistical multiplexer 808combines the three input bit streams into a single bit stream at itsoutput. Through use of these feedback lines 812, 814 and 816, thestatistical multiplexer 808 is able to provide a control input toselectively activate the bit rate converters 802, 804, 806 according tothe available bandwidth in the channel 810. In the preferred embodimentof the present invention, the statistical multiplexer 808 outputs a datastream that is an MPEG2 transport stream and conforms to the standardMPEG2 format. The statistical multiplexer 808 may have a variety ofembodiments and use different algorithms or bases to perform themultiplexing. For example, specific bit streams may be designated tohave a priority in receiving a certain percentage of channelavailability. Just as an example, video bit stream 1 may have apriority, and therefore be controlled via line 812 to have a minimumamount of rate conversion, while the other video bit streams 2 and 3,may have lower priorities, and therefore be subject to greater bit rateconversion using lines 814, 816. Furthermore, the statisticalmultiplexer 808 may also use time of transmission or scene content forvideo data to determine the priorities for channel usage, and use thecontrol lines 812, 814, and 816 accordingly to apply various bitconversions rates to maintain maximum use of the channel capacity. In analternate embodiment, the statistical multiplexers may be of the typeconstructed by General Instruments, DiviCom and other companies tocontrol real-time encoders. While the system 800 is shown asmultiplexing between only three input streams, those skilled in the artwill recognize that any number of streams could be multiplexed. Finally,the output of the statistical multiplexer 808 is coupled to the channel810.

Referring now to FIG. 9, a third embodiment of a system 900 fortransporting video data integrated within the communication channel, inparticular, for a rate adaptive asymmetric digital subscriber line(RADSL), is shown. The present invention is directed toward theintegration of bit rate conversion schemes with ADSL rate adaptationfeature to achieve relatively lossless transmission. Therefore, one keyelement of the invention is to create a synergy between the bit rateconversion of compressed video bit stream and the use of RADSL totransport compressed video bit stream, especially the transform codingbased (such as MPEG) compressed video bit stream. Throughout the presentapplication, the term bit rate conversion has been used so as not topreclude the possibility of upward bit rate conversion, but in generalpractical applications, the need for downward rate conversion farexceeds the need for upward rate conversion. Upward bit rate conversioncan be achieved quite easily in different layers above the videocompression layer, such as the transport layer (null transport packets),ADSL layer (bearer channel capacity configuration), etc.

As shown in FIG. 9, the third embodiment of the system 900 comprises anintegrated bit conversion and transmitter device 902, a physical medium18, a rate adaptive digital subscriber loop (RADSL) receiver 208 andinitialization & reconfiguration logic 908. As shown, the integrated bitconversion and transmitter device 902 further comprises a bit rateconversion device 904 and a rate adaptive digital subscriber loop(RADSL) transmitter 906. The bit rate conversion device 904 has a datainput and an output, and is coupled to receive a compressed bit streamat the input on line 210. The output of the bit rate conversion device904 is coupled to the input of the RADSL transmitter 906 by line 910.The bit rate conversion device 904 also has a control input coupled toreceive a control signal from the RADSL transmitter 906 by line 912.Thus, the conversion rate by which the compressed bit stream is reducedor increased is controlled by the signal from the RADSL transmitter 906.For example, the bit rate conversion device 904 may be of the typedescribed above with reference to FIGS. 4 and 5.

Next, the RADSL transmitter 906 processes the bit stream from line 910and outputs a bit stream over the physical medium 18. The RADSLtransmitter 906 is of a conventional type (for example, the RADSLtransmitter 906 may be a Copper Gold ADSL chip manufactured by Motorola,Inc. of Schaumburg, Ill.), and as will be described below with referenceto FIG. 10; however, it is adapted to provide control signals to the bitrate conversion device 904. In particular, the RADSL transmitter 906 ismodified from a conventional type by providing an output for passingalong rate control signals received at initialization or duringoperation. A conventional RADSL transmitter is coupled to receive bitrate change control signals at either initialization or on-line mode.The control signal is in the form of bit rate value that the RADSLtransmitter can handle. In one embodiment, this value is passed on tothe bit rate conversion device 904 using line 912 to determine thetargeted bit rate. Those skilled in the art will realize that the methodfor passing this rate control signal form the RADSL transmitter 906 tothe bit rate conversion device 904 is implementation specific and may bedone using any one of a number of conventional techniques.

The bit stream passes over the physical medium 18 to the input of theRADSL receiver 208. The RADSL receiver 208 is of a conventional type,and converts the information to a compress bit stream format which isoutput on line 214. As shown, the RADSL transmitter 906, the physicalmedium 18, and the RADSL receiver 208 are each coupled to initialization& reconfiguration logic 908 by line 914 to receive control signals as tohow the data is to be coded and decode before and after transmissionover the medium 18. The line 914 is also used to test the medium todetermine capacity of the channel or medium 18.

While the initialization & reconfiguration logic 908 is depicted in FIG.9 as a logic block, those skilled in the art will recognize that theinitialization & reconfiguration logic in box 908 may be a suite ofsignaling protocols exchanged between the RADSL receiver 208 and theRADSL transmitter 906 so that each device knows what is the maximumachievable bit rates in each directions, such as is now conventionallydone is RADSL channels, and is an integral part of the ADSL standard.

RADSL adapts the maximum channel capacity to the physical twisted wire18 line condition by adjusting the coding configuration. In the presentinvention, the bit rate conversion device 904 is integrated with theRADSL transmitter 906 and is used to adjust the output bit rate downfrom the input rate R to R₁ (typically R₁≦R). This ensures that when thecompressed video bit stream is received at the RADSL receiver 204(decoder), the resulting bit stream maintains its data integrity andthus yields graceful quality degradation.

In the present invention, the channel capacity supported by the ADSLchannel is advantageously conveyed to the rate conversion device 904during the initialization stage. In addition, on-line adaptation andreconfiguration of the supported rate must also be conveyed to the rateconversion device 904. For example, with the ANSI (DMT) implementation,the maximum channel capacity the link can support at initial connectionis signaled from the RADSL receiver 208 to the RADSL transmitter 906 inthe R-B&G phase of the initialization process. In ANSI implementation,on-line adaptation and reconfiguration of bit rate are signaled via theADSL overhead control (aoc) channel and the channel capacity can beincreased in minimum steps of 4 kbps at an interval of 17 ms to about 43sec selectable by the RADSL receiver 208. This provides sufficientflexibility to the rate conversion device to properly setup the ratecontrol parameters to perform the rate conversion.

Referring now to FIG. 10, a graphical representation of the referencemodel used for the RADSL transmitter 906 and an RADSL receiver 208 isshown. ADSL is becoming widely deployed by major telephone companies andone particular implementation of ADSL, the Discrete Multi-Tone (DMT),has been standardized by the American National Standards Institute(ANSI). In this standard, provisions are made to allow transmitter andreceiver to perform initialization, training, optimum bit rateconfiguration, bit rate changes, etc. ADSL standard based on DMT ismodeled as ADSL Transceiver Unit-Central office (ATU-C) and ADSLTransceiver Unit-Remote terminal (ATU-R). This model is shown in moredetail in FIG. 10. From the model of FIG. 10, those skilled in the arewill recognize that the RADSL receiver 208 has the same component blocksto perform the inverse function in ordered in reverse. The RADSLtransmitter 906 preferably comprises a multiplexing and synchronizationcontroller 1000, a error correction and interleaver 1002, aconstellation encoder 1004 and a DAC and analog signal processor 1006.The bit stream is received by the multiplexing and synchronizationcontroller 1000 which adds or removes control and synchronizationinformation from the bit stream. The multiplexing and synchronizationcontroller 1000 is coupled to the error correction and interleaver 1002which performs error correction such as a cyclic redundancy checking andforward error correction. The output of the error correction andinterleaver 1002 is in turn coupled to the constellation encoder 1004which performs encoding on the bit stream. Finally, the bit stream inconverted to an analog signal, processed and applied to the physicalmedium 18 by the DAC and analog signal processor 1006.

Yet another application of the present invention is to AsynchronousTransfer Mode (ATM) networks. The present invention also includes theconcept of traffic shaping, used on ATM networks to change the bit rateprofile of ATM cell streams through the bit rate conversion ofcompressed video and has tremendous value in all future ATM networkimplementations. Traffic shaping within the ATM networks usingcompressed video bit rate conversion is a crucial enabler of flexiblytransport MPEG-2 video, as well as any other types of compressed videostreams, over ATM networks. The present invention creates a synergybetween the bit rate conversion of compressed video bit stream and theuse of ATM networks to transport compressed video bit stream, especiallythe transform coding based (such as MPEG) compressed video bit stream.

Referring now to FIG. 11, another embodiment of the present invention asapplied to an asynchronous transfer mode (ATM) network is shown. FIG. 11is a block diagram of a system using the rate conversion device of thepresent invention as an input point for an asynchronous transfer mode(ATM) network 1106. In this embodiment, the present invention includesan integrated bit rate conversion device and ATM cell converter 1100which in turn is coupled to an ATM network 1106. The ATM network 1106 isa conventional type known to those skilled in the art. The integratedbit rate conversion device and ATM cell converter 1100 further comprisesa bit rate conversion device 1102 and an ATM cell converter 1104. Thebit rate conversion device 1102 is similar to those that have beendescribed above with reference to FIGS. 4 and 5. However, as shown inFIG. 11, the conversion rate is controlled by an external ratecontroller 1108 that is coupled to the bit rate conversion device 1102by line 1110. In one embodiment, the external rate controller 1108 islogic or software that generates a control signal to specify aconversion rate that bit rate conversion device 1102 implements. Theexternal rate controller 1108 can provide external commands for settinga target bit rate out of the bit rate conversion device 1102. The targetbit rate out of the bit rate conversion device 1102 may be set based onseveral factors such as congestion condition within the ATM network1106, connection level bandwidth negotiation between user and thenetwork provider, etc. In yet another embodiment, the external ratecontroller 1108 receives control signals from the ATM network 1106 suchas depicted in FIG. 1 by line 1112, for example from a remote networknode. Such a remote node (not shown) can use the underlying conventionalATM signal protocol to provide rate control signals to the external ratecontroller 1108, as will be understood to those skilled in the art.

In this scenario, compressed video bit stream, such as MPEG-2 transportstream containing video programs, is being transported through the ATMnetworks from one location to another. In this case, rate conversionscheme is used with the ATM networks to accommodate the bit ratedifferences between available connection capacity from the ATM networksand the bit rate of the incoming MPEG-2 transport stream when theconnection to be established is constant bit rate (CBR). This scheme isimplemented at the ingress point of the ATM networks. Once the bit rateconversion device 1102 has converted the compressed video bit stream toa rate suitable for the ATM network 1106, the converted bit stream isprovided to the ATM cell converter 1104. The ATM cell converter 1104packetizes the converted bit stream into fixed sized data units or cellsin a conventional manner. The ATM cell converter 1104 preferablyperforms the conversion from MPEG2 transport packets into ATM cells. InATM terms, this function is called segmentation and reassembly (SAR),and is part of the ATM adaptation layer protocols (AAL). A typicalimplementation of the AAL function is in the form of an ASIC chip. Theoutput cells are provided by the ATM cell converter 1104 to the ATMnetwork 1106 and send to their destination.

FIG. 12 is a block diagram of a system integrating the rate conversiondevice of the present invention into an asynchronous transfer mode (ATM)switch. As shown in FIG. 12, the preferred embodiment of for theintegrated ATM converter and bit rate conversion unit 1200 comprises anATM cell de-converter 1202, a bit rate conversion device 1204, and anATM cell converter 1206. In this embodiment, the integrated ATMconverter and bit rate conversion unit 1200 is used to smooth the bitrate profile of the virtual connection at the ingress to the ATM networkso that the resulting bit rate profile of the connection can be admittedby the ATM network. The integrated ATM converter and bit rate conversionunit 1200 can also be used to smooth the bit rate profile within the ATMnetwork at point of traffic congestion so that buffers within thenetwork will not drop cells at times of network congestion. This schemeis implemented within the ATM network, normally co-located with the ATMcross connection (ATM switches) devices where congestion conditionrequires re-allocation of bandwidth.

The ATM cell de-converter 1202 has an input and an output, and receivesATM cells for further distribution over the ATM network 1208. The ATMcell de-converter 1202 removes the data from its packetized format andrestores it to a bit stream of compressed data, which is provided at theoutput of the ATM cell de-converter 1202. The output of the ATM cellde-converter 1202 is coupled to the input of the bit rate conversiondevice 1204. The ATM cell de-converter 1202 can be any one of a numberof conventional type devices know in the art. The bit rate conversiondevice 1204 is as has been described above in FIGS. 4 and 5. The bitrate conversion device 1204 changes the bit rate and provide theconverted bit stream to the ATM cell converter 1206. The ATM cellconverter 1206 takes the converted bit stream and then packetizes theconverted bit stream into fixed sized data units or cells in aconventional manner. The output cells are provided by the ATM cellconverter 1206 to the ATM network 1208.

Finally, referring now to FIG. 13, a block diagram of a system 1300integrating the rate conversion device of the present invention into anATM/ADSL communication device is shown. In this embodiment, the rateconversion scheme is used when compressed bit stream is carried aspayload of the ATM cell stream, which in turn is transmitted over theRADSL device from the CO to the remote site. In this case, rateconversion is required not because of lack of connection bandwidthwithin the ATM networks or because of congestion conditions within theATM networks. The rate conversion is required because the availablebandwidth on the RADSL may be smaller than the bit rate of thecompressed bit stream. In this case, the RADSL receiver must alsoperform the segmentation and re-assembly (SAR) of ATM cells beforesending the video bit stream to the digital decoder.

As shown in FIG. 13, the system 1300 preferably comprises an ATM network1302, an integrated ATM converter and bit rate conversion unit 1304, aRADSL transmitter 1306, a physical medium 18 and a RADSL receiver 1308.The ATM network is a conventional type known in the art, and providesATM cells to the input of the integrated ATM converter & bit rateconversion unit 1304. The integrated ATM converter & bit rate conversionunit 1304 is similar to the type described above with reference to FIG.12, and comprises an ATM cell de-converter 1310, a bit rate conversiondevice 1312, and an ATM cell converter 1314. The ATM cell converter 1314is different than the one described above in FIG. 12 because it receivesa control input from the RADSL transmitter via line 1316, in addition toproviding the data stream to the RADSL transmitter via line 1318. Inparticular, as shown in FIG. 13, the signal line 1316 is preferablycoupled between the bit rate conversion device 1312 and the RADSLtransmitter 1306. The signal line is used to pass the rate controlsignals to the bit rate conversion device 1312 in a manner similar thatdescribed above with reference to FIG. 9. The RADSL transmitter 1306,physical medium 18 and RADSL receiver 1308 are similar to that describedabove with reference to FIG. 9. The notable differences are that theRADSL transmitter 1306 provides feedback information, and the RADSLreceiver 1308 performs the segmentation and re-assembly (SAR) of ATMcells as has been noted above. Those skilled in the art will recognizethat FIG. 13 describe the transmission of data only in one directionfrom 1302 to 1308, and that the RADSL transmitter 1306 and RADSLreceiver 1308 are actually transceiver for transmission of data andvideo in the opposite direction similar to conventional RADSL channel.For such a reverse direction from 1308 to 1302, FIG. 13 could alsoinclude a second integrated ATM converter & bit rate conversion unit1304 (not shown).

While the present invention has been described with reference to certainpreferred embodiments, those skilled in the art will recognize thatvarious modifications may be provided. For example, the presentinvention may be used to perform bandwidth sharing, despite the factthat the available bandwidth from the transmission facility, whichincludes but is not limited to, xDSL, ATM, wireless channel, issufficient to send the incoming compressed bit stream. In general, fordata traffic, such as TCP/IP based traffic, the data bit rate cannot bedetermined. In addition, the video bit stream may not have constant bitrate, therefore, the resulting total bandwidth cannot be determinedbefore the connection is established. The application of bit rateconversion, however, will ensure that the resulting total bandwidth willalways be less than the total available channel bandwidth. To this end,some kind of priority scheme must also be used to ensure that no videodata is lost. Specifically, when the total input bit rate exceed thechannel capacity, TCP/IP based data packets must be discarded by thetransmission facility to ensure packets containing video data is notlost. Therefore, there is a trade-off between how much bit ratereduction should be performed to the video bit stream, which results ingraceful degradation of video quality, and how much throughput should bemade available to TCP/IP based data streams. These and other variationsupon and modifications to the preferred embodiments are provided for bythe present invention.

1. An apparatus for providing compressed video data onto a network, theapparatus comprising: a bit rate converter having an input, a controlinput and an output, the input coupled to receive a first bitstreamhaving a first bit rate; the bit rate converter being operable todynamically adjust at least one quantization factor of the firstbitstream to thereby convert the first bitstream into at least one of aplurality of different bitstreams having different bit rates, includinga second bitstream having a second bit rate, different from the firstbit rate, the second bitstream being provided at the output of the bitrate converter; a rate controller coupled to the control input of thebit rate converter and operable to control the bit rate converter byproviding bit rate information regarding the second bit rate to the bitrate converter; wherein the bit rate converter is further operable todynamically adjust the at least one quantization factor of the firstbitstream using at least a portion of the bit rate information; and atransmitter coupled to receive the second bitstream having the secondbit rate and to transmit the second bitstream onto the network.
 2. Theapparatus of claim 1 wherein the bit rate converter is further operableto convert the first bitstream to a third bitstream having a third bitrate, different from the first and second bit rates, the third bitstreambeing provided at the output of the bit rate converter; and wherein thebit rate converter is further operable to dynamically adjust the atleast one quantization factor of the first bitstream using at least aportion of the bit rate information provided by the rate controller tothereby convert the first bitstream into the third bitstream.
 3. Theapparatus of claim 1 wherein the rate controller is coupled to a linethat receives a control signal indicating one of the second bit rate andan amount of bit rate conversion for the first bitstream.
 4. Theapparatus of claim 3 wherein the rate controller is external to theapparatus and the line receives the second bit rate from an ATM network.5. The apparatus of claim 3 wherein the transmitter is a RADSLtransmitter and wherein the line is coupled to the RADSL transmitter andreceives the second bit rate from the RADSL transmitter.
 6. Theapparatus of claim 1 wherein the bit rate converter comprises a set ofmodification units.
 7. The apparatus of claim 6 wherein the modificationunits includes at least one of: a modification unit capable of reducingthe number of bits needed for discrete cosine transform coefficients, amodification unit capable of reducing the number of bits needed formotion vectors, and a modification unit capable of reducing the numberof bits needed for auxiliary information.
 8. The apparatus of claim 6wherein the rate controller provides a bit rate control signal to eachof the modification units.
 9. The apparatus of claim 1 wherein thesecond bitstream comprises MPEG compressed video data.
 10. An apparatusfor providing compressed video data onto a network, the apparatuscomprising: a bit rate converter operable to dynamically adjust at leastone quantization factor of a first bitstream to thereby convert thefirst bitstream into at least one of a plurality of different bitstreamshaving different bit rates, including a second bitstream having a secondbit rate, different from the first bit rate, the second bitstream beingprovided at an output of the bit rate converter; a rate controllercoupled to the control input of the bit rate converter and operable tocontrol the bit rate converter by providing bit rate informationregarding the second bit rate to the bit rate converter; a transmittercoupled to receive the second bitstream having the second bit rate andto transmit the second bitstream onto the network; wherein the bit rateconverter is further operable to dynamically adjust the at least onequantization factor of the first bitstream using at least a portion ofthe bit rate information; wherein the bit rate converter comprises a setof modification units including a first modification unit operable toreceive a bit rate control signal from the rate controller; and whereinthe first modification unit is further operable to use the bit ratecontrol signal to dynamically adjust quantization processing performedby the first modification unit in a manner which results in achievementof the second bit rate for the second bitstream.
 11. The apparatus ofclaim 10 wherein the bit rate converter is further operable to convertthe first bitstream to a third bitstream having a third bit rate,different from the first and second bit rates, the third bitstream beingprovided at the output of the bit rate converter; and wherein the bitrate converter is further operable to dynamically adjust the at leastone quantization factor of the first bitstream using at least a portionof the bit rate information provided by the rate controller to therebyconvert the first bitstream into the third bitstream.
 12. The apparatusof claim 10 wherein the second bitstream comprises MPEG compressed videodata.
 13. An apparatus for providing compressed video data onto anetwork, the apparatus comprising: a first bit rate converter operableto dynamically adjust at least one first quantization factor of a firstbitstream to thereby convert the first bitstream into a second bitstreamhaving a second bit rate, the second bitstream being provided at anoutput of the first bit rate converter; a second bit rate converteroperable to dynamically adjust at least one second quantization factorof a third bitstream to thereby convert the third bitstream into afourth bitstream having a fourth bit rate, the fourth bitstream beingprovided at an output of the second bit rate converter; a multiplexeroperable to receive the second and fourth bitstreams, and furtheroperable to generate a multiplexed output bitstream using the second andfourth bitstreams, the multiplexed output bitstream having a fifth bitrate associated therewith; a rate controller coupled to the multiplexerand operable to provide bit rate information relating to a target bitrate of the multiplexed output bitstream; wherein the multiplexer isfurther operable to provide control information to first and second bitrate converters for selectively controlling operation of the first andsecond bit rate converters in order to cause the fifth bit rate of themultiplexed output bitstream to substantially match the target bit rate;wherein the first and second bit rate converters each include arespective control input coupled to receive the control information;wherein the first bit rate converter is operable to use at least aportion of the control information to dynamically adjust a value of thesecond bit rate of the output of the first bit rate converter; andwherein the second bit rate converter is operable to use at least aportion of the control information to dynamically adjust a value of thefourth bit rate of the output of the second bit rate converter.
 14. Theapparatus of claim 13 being further operable to: identify a firstchannel of the network for use in transporting data from the multiplexedoutput bitstream; dynamically and periodically determine updatedavailable bandwidth information relating to an available bandwidth ofthe first channel; and determine, using the updated available bandwidthinformation, the target bit rate of the multiplexed output bitstream.15. The apparatus of claim 13 being further operable to: identify afirst channel of the network for use in transporting data from themultiplexed output bitstream; dynamically and periodically determineupdated available connection capacity information relating to anavailable connection capacity of the first channel; and determine, usingthe updated available connection capacity information, the target bitrate of the multiplexed output bitstream.
 16. An apparatus for providingcompressed video data onto a network, the apparatus comprising: a firstbit rate converter having an input, a control input and an output, theinput coupled to receive a first bitstream having a first bit rate, thefirst bit rate converter being operable to dynamically adjust at leastone quantization factor of the first bitstream to thereby convert thefirst bitstream into a second bitstream having a dynamically adjustableoutput bit rate, different from the first bit rate, the second bitstreambeing provided at the output of the first bit rate converter; and atransmitter coupled to receive the second bitstream and operable totransmit the second bitstream onto a first channel of the network, thefirst channel having associated therewith first channel criteria, thefirst channel criteria including at least one criteria selected from agroup consisting of: first channel bit rate criteria, and first channelavailable bandwidth criteria; the apparatus being operable to:dynamically and periodically determine, using at least a portion of thefirst channel criteria, an updated target bit rate value; and providetarget bit rate control information to the control input of the firstbit rate converter, wherein the target bit rate control informationincludes information relating to the updated value for the target bitrate of the second bitstream; the first bit rate converter being furtheroperable to dynamically adjust the at least one quantization factor ofthe first bitstream using at least a portion of the target bit ratecontrol information to thereby cause the dynamically adjustable outputbit rate of the second bitstream to substantially match the updatedvalue of the target bit rate.
 17. The apparatus of claim 16 wherein thefirst bit rate converter is further operable to convert the firstbitstream to a third bitstream having a third bit rate, different fromthe first and dynamically adjustable output bit rates, the thirdbitstream dynamically adjust at least one quantization factor of thefirst bitstream to thereby convert the first bitstream into at least oneof a plurality of different bitstreams having different bit rates,wherein the bit rate converter is further operable to dynamically adjustthe at least one quantization factor of the first bitstream using atleast a portion of the bit rate information; being provided at theoutput of the first bit rate converter.
 18. The apparatus of claim 16,wherein the transmitter is an xDSL transmitter and wherein the firstchannel is a twisted copper wire.
 19. The apparatus of claim 16, whereinthe transmitter includes an ATM cell converter, the network includes anATM network, and the first channel corresponds to a channel of the ATMnetwork; wherein the updated target bit rate value is substantiallyequal to an available connection capacity within the ATM network; andwherein the dynamically adjustable output bit rate is greater than 9600samples/second.
 20. The apparatus of claim 16 further comprising areceiver coupled to a physical medium included in the first channel. 21.The apparatus of claim 20 wherein the receiver is an RADSL receiverhaving an input and an output, the input of the RADSL receiver coupledto the physical medium.
 22. The apparatus of claim 16 wherein the secondbitstream comprises MPEG compressed video data.
 23. The apparatus ofclaim 16 being further operable to: output the second bitstreamaccording to an xDSL protocol.
 24. The apparatus of claim 16 beingfurther operable to: output the second bitstream according to an RADSLprotocol.
 25. The apparatus of claim 16 further comprising: a ratecontroller operable to receive first channel information relating to thefirst channel criteria, and operable to generate the target bit ratecontrol information using at least a portion of the first channelinformation.
 26. A method for modifying a bit rate of a bitstream to usean available bandwidth of a first channel, the first channel havingassociated therewith first channel criteria, the first channel criteriaincluding at least one criteria selected from a group consisting of:first channel bit rate criteria, and first channel available bandwidthcriteria, the method comprising: (a) dynamically converting, using afirst bit rate converter, a first bitstream having a first bit rate to asecond bitstream having a dynamically adjustable output bit rate,different from the first bit rate, said dynamically convertingcomprising: receiving, at the first bit rate converter, the firstbitstream at the first bit rate; receiving a control signal whichincludes information relating to a target bit rate value for thedynamically adjustable output bit rate; dynamically adjusting, using thetarget bit rate value information and the first bit rate converter, atleast one quantization factor of the first bitstream to thereby convertthe first bitstream into the second bitstream having the dynamicallyadjustable output bit rate; outputting the second bitstream; and (b)transmitting the second bitstream on the first channel.
 27. The methodof claim 26, said dynamically converting further comprising: dynamicallyand periodically determining, using at least a portion of the firstchannel criteria, an updated target bit rate value; and dynamicallyadjusting, using the updated target bit rate value, at least onequantization factor of the first bitstream to thereby convert the firstbitstream into the second bitstream, wherein the bit rate of the secondbitstream substantially matches the updated target bit rate value. 28.The method of claim 26, said dynamically converting further comprising:dynamically determining, using at least a portion of the first channelcriteria, an updated target bit rate value; and dynamically adjusting,using the updated target bit rate value, at least one quantizationfactor of the first bitstream to thereby cause the dynamicallyadjustable output bit rate of the second bitstream to substantiallymatch the updated target bit rate value.
 29. The method of claim 26further comprising outputting the second bitstream according to an xDSLprotocol.
 30. The method of claim 26 further comprising outputting thesecond bitstream according to an RADSL protocol.
 31. The method of claim26 further comprising: calculating the target bit rate value usinginformation relating to the first channel available bandwidth criteria.32. A method for providing compressed video data onto a first channel ofa network, the first channel having associated therewith first channelcriteria, the first channel criteria including at least one criteriaselected from a group consisting of: first channel bit rate criteria,and first channel available bandwidth criteria, the method comprising:(a) dynamically converting, using a first bit rate converter, a firstbitstream including the video data at a first bit rate to a secondbitstream including the video data at a dynamically adjustable outputbit rate, different from the first bit rate, said converting comprising:receiving, at the first bit rate converter, the first bitstream at thefirst bit rate; receiving a control signal which includes informationrelating to a target bit rate value for the dynamically adjustableoutput bit rate; dynamically adjusting, using the target bit rate valueinformation and the first bit rate converter, at least one quantizationfactor of the first bitstream to thereby convert the first bitstreaminto the second bitstream having the dynamically adjustable output bitrate; outputting the second bitstream; and (b) transmitting the secondbitstream over the first channel.
 33. The method of claim 32, saiddynamically converting further comprising: dynamically and periodicallydetermining, using at least a portion of the first channel criteria, anupdated target bit rate value; and dynamically adjusting, using theupdated target bit rate value, at least one quantization factor of thefirst bitstream to thereby convert the first bitstream into the secondbitstream, wherein a bit rate of the second bitstream substantiallymatches the updated target bit rate value.
 34. The method of claim 32,said dynamically converting further comprising: dynamically determining,using at least a portion of the first channel criteria, an updatedtarget bit rate value; and dynamically adjusting, using the updatedtarget bit rate value, at least one quantization factor of the firstbitstream to thereby cause the dynamically adjustable output bit rate ofthe second bitstream to substantially match the updated target bit ratevalue.
 35. The method of claim 32 further comprising outputting thesecond bitstream according to an xDSL protocol.
 36. The method of claim32 outputting the second bitstream according to an RADSL protocol. 37.The method of claim 32 further comprising: calculating the target bitrate value using information relating to the first channel availablebandwidth criteria.
 38. A method for providing compressed video dataonto at least one channel of a network, the method comprising:receiving, from a first channel, a first bitstream having a first bitrate, the first bitstream including video data; identifying a secondchannel for use in transporting a second bitstream which includes atleast a portion of the video data, the second channel having associatedtherewith second channel criteria, the second channel criteria includingat least one criteria selected from a group consisting of: secondchannel bit rate criteria, and second channel available bandwidthcriteria; dynamically and periodically identifying, using at least aportion of the second channel criteria, an updated target bit rate valuefor the second bitstream; dynamically adjusting, using the updatedtarget bit rate value and at least one bit rate converter, at least onequantization factor of the first bitstream to thereby convert the firstbitstream into the second bitstream, wherein a bit rate of the secondbitstream substantially matches the updated target bit rate value;outputting the second bitstream; and transmitting the second bitstreamover the second channel.
 39. The method of claim 38 further comprising:calculating the target bit rate value using information relating to thefirst channel available bandwidth criteria.
 40. The method of claim 38further comprising: receiving the updated bit rate value from a devicein an ATM network.
 41. The method of claim 38 further comprising:receiving the updated bit rate value from a RADSL transmitter.
 42. Asystem for providing compressed video data onto at least one channel ofa network, the method comprising: at least one processor; at least oneinterface; memory; means for receiving, from a first channel, a firstbitstream having a first bit rate, the first bitstream including videodata; means for identifying a second channel for use in transporting asecond bitstream which includes at least a portion of the video data,the second channel having associated therewith second channel criteria,the second channel criteria including at least one criteria selectedfrom a group consisting of: second channel bit rate criteria, and secondchannel available bandwidth criteria; means for dynamically andperiodically identifying, using at least a portion of the second channelcriteria, an updated target bit rate value for the second bitstream;means for dynamically adjusting, using the updated target bit ratevalue, at least one quantization factor of the first bitstream tothereby convert the first bitstream into the second bitstream, wherein abit rate of the second bitstream substantially matches the updatedtarget bit rate value; means for outputting the second bitstream; andmeans for transmitting the second bitstream over the second channel.